Switching regulator

Abstract

The present invention provides a switching regulator for controlling the overshoot voltage which is generated during transition from power ON, when soft start activates, to normal operation, when the load side output is maintained at the output setting voltage by the feedback circuit. A clamp circuit is disposed between a soft start circuit and an error amplifier, an upper limit value from the output of the soft start circuit (SS) to the output of the error amplifier (FB) is set, so that the rise of voltage of the output of the error amplifier (FB) is controlled when power is turned ON, and time until the output of the error amplifier (FB) is stabilized is decreased, by which the overshoot voltage generated in the load side output (VOUT) is controlled.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a switching regulator for supplying power from the power supply to the load side via a switching element, with which a predetermined voltage at the load side (output setting voltage) can be acquired by switching this switching element under a predetermined control, and more particularly to a switching regulator that has a soft start function.[0003]2. Description of the Related Art[0004]As one system of acquiring output setting voltage, a switching regulator system, which switches a switching element under a predetermined control, has been conventionally used since it is compact and can implement high efficiency. In order to control rush current which flows into the switching element when power is turned ON, a soft start operation is executed (e.g. Japanese Patent Application Laid-On No. 7-336999).[0005]FIG. 6 is a circuit diagram of a conventional switching regulator. In the switching re...

AI Technical Summary

Benefits of technology

[0016]Since the upper limit value from the output of the soft start circuit to the output of the error amplifier is set by this clamp circuit, the rise of the output voltage of the error amplifier is controlled when power is turned ON, and time until the output of the error amplifier stabilizes can be decreased, and therefore the overshoot voltage to be generated in the load side output is controlled.

[0018]This clamp circuit has a small number of composing elements, so an area occupied by the clamp circuit in a semiconductor integrated circuit can be decreased. Also since the number of composing element is small, the difference of the emitter-base voltages generated by the difference of the emitter-base junction areas can be adjusted relatively simply.

[0020]In this clamp circuit, the voltage generated by the current flowing through the resistor is also included in the factors of setting the clamp voltage, so it is possible to increase the emitter-base junction area of the first transistor, which is related to the output of the error amplifier, and voltage can be sufficiently clamped even if the drive capability of the error amplifier is large.

Problems solved by technology

Along with this, the load side output (VOUT) stabilizes at the output setting voltage, but a high overshoot voltage is generated during this time.

Also this high overshoot voltage has the danger of damaging the devices related to the load side output (VOUT).

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